The present invention relates to a rotary head assembly of a video tape recorder (to be referred as "VTR set" in this specification) and more particularly the construction of a bearing or thrust support for supporting a rapidly spinning rotor of the rotary head assembly which carries heads.
The VTR rotary head assembly must satisfy the following two stringent requirements:
(1) Variations in rotational speed must be kept minimum; and PA1 (2) Longitudinal and transverse vibrations must be reduced to a minimum. PA1 (1) It is difficult to design and construct a VTR rotary head assembly which is compact in size, light in weight and inexpensive to manufacture. PA1 (2) It is difficult to design and construct a liquid bearing to seal a lubricant for a long time and to ensure the precision rotation of the rotor of the rotary head assembly. PA1 (3) The liquid bearing must ensure the precision rotation of the rotor over a long period. PA1 (4) Furthermore, the trend toward the high-density recording requires that the rotor must spin very rapidly at a further higher degree of accuracy. In addition, it is preferable that the rotor can be spun with low resistant torque.
In addition, the prior art rotary head assembly of the type in which the rotor is supported by ball bearings or the like cannot satisfy the requirements for achieving a long recording and reproducing time by recording the video and sound signals at an extremely high density on the tape or for making the VTR sets, specially portable sets, compact in size and light in weight.
In order to overcome the above and other problems encountered in the prior art rotary head assembly, the use of liquid bearings has been proposed. However the following problems are present.
The domestic electrical and electronic equipment such as VTR sets must be compact in size and light in weight and mass produced at low cost. Industrial VTR rotary head cylinders of the type using air bearings have been long used, but they must be provided with a compressed air source such as a compressor and a pneumatic control circuit which is very complex in construction. Therefore, the development of such industrial VTR rotary head assembly into domestic VTR rotary head assembly is very difficult.
In addition, the recent demand for portable VTR sets is very strong. Since the height of the portable VTR set is dependent upon that of the rotary head assembly used, there is a strong demand for a VTR rotary head assembly which is compact in size and light in weight.
In the case of machine tools, the lubricating oil can be exchanged or supplemented at any time, but in the case of the domestic electronic or electrical appliances or equipment such as VTR sets, the lubricating oil must be completely sealed so as to avoid the necessity of relubrication.